title: Effectiveness of seasonal influenza vaccine in preventing medically attended influenza infection in England and Wales during the 2010/2011 season: a primary care-based cohort study.
abstract: BACKGROUND
  Estimates of seasonal influenza vaccine effectiveness (VE) are affected by factors such as the strain of the current circulating influenza virus and characteristics of the host.
  
  
  OBJECTIVE
  The objective of this study was to provide VE estimates for the 2010/2011 seasonal trivalent influenza vaccine (TIV) in preventing medically attended influenza in England and Wales for the season 2010/2011.
  
  
  METHODS
  A cohort study design was employed using electronic health records extracted from 104 GP practices in the Royal College of General Practitioners (RCGP) primary care sentinel network. Endpoints included influenza-like illness (ILI), lower respiratory tract infection (LTRI) as well as PCR-confirmed influenza from patients swabbed from practices participating in a swabbing scheme. Adjustment was made for age, month, underlying chronic condition, region and number of consultations in the 12 months prior to the study period. In addition to the cohort analysis, a nested test-negative case-control analysis (TNCC) was carried out using the swab-negative results as controls.
  
  
  RESULTS
  In the cohort analysis, VE against LRTI was -0·5% [95% CI: (-7·0%, 7·5%)], against ILI was 37·8% [95% CI: (32·3%, 43·0%)] and against PCR-confirmed influenza was 50·0% [95% CI:(25·9%, 65·6%)] for type A and 44·4% [95% CI: (10·1%, 65·6%)] for type B. Using the TNCC design, the type A VE was 56·5% [95% CI: (30·4%, 72·7%)] and for type B was 54·0% [95% CI: (21·0%, 73·3%)].
  
  
  CONCLUSIONS
  This study shows that the 2010/2011 TIV provided moderate protection against the circulating influenza strains for the 2010/2011 season. It also suggests that VE against the less specific diagnosis of ILI can be found, but less specific endpoints such as LRTI are not useful.
authors.affiliation: Statistics Unit, Public Health England, London, UK.
authors.forename: George
authors.initials: G
authors.lastname: Kafatos
authors.forename: Richard
authors.initials: R
authors.lastname: Pebody
authors.forename: Nick
authors.initials: N
authors.lastname: Andrews
authors.forename: Hayley
authors.initials: H
authors.lastname: Durnall
authors.forename: Michele
authors.initials: M
authors.lastname: Barley
authors.forename: Douglas
authors.initials: D
authors.lastname: Fleming
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D011320:Primary Health Care / Q000706:statistics & numerical data; D014852:Wales / Q000453:epidemiology; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: Cohort; influenza; trivalent influenza vaccine; vaccine effectiveness